The brief answer: No surprise; a duck's quack will echo.
This subject (with report of confirming experiment) has been covered by
the column the Straight Dope and can be found at http://www.straightdope.com/columns/980522.html
It was also in one of the recent books of collections of the column
although I don't remember which one. Buy them all and support these
people.
I recommend the column for its willingness to answer such questions
seriously, albeit humorously.
THO
Thomas O'Neill
o'neill@csvrgs.k12.va.us
Physics
oneill@csvrgs.k12.va.us
C Shenandoah Valley R. Governor's School (540) 245
5088
Fishersville, Virginia 22939